Heretofore, high-molecular weight compounds containing primary amino groups in their side chains have been effectively utilized in various industrial fields because of their high reactivity, that is, because they can easily react with functional groups such as aldehyde, ketone, alkyl halide, isocyanate, thioisocyanate, active double bond, epoxy compound, cyanamide, guanidine, urea, acid, acid anhydride, and acyl halide.
As such high-molecular weight compounds containing primary amino groups in their side chains, there have been heretofore known polyvinylamine produced by hydrolysis of poly-N-vinylacetamide or poly-N-vinylformamide and polyallylamine produced by polymerization of a hydrochloride of allylamine.
However, in the case where these methods are used to prepare a high-molecular weight compound, although a polymer or copolymer containing a primary amino group can be obtained, its molecular weight is not so great as intended, and these methods require radical polymerization of an amine or an amine precursor as a monomer which limits the kind of monomers to be copolymerized therewith. Therefore, these high-molecular weight compounds may not fully exert their effects in some applications.
As examples of copolymers containing amino groups in their side chains, there are disclosed in JP-A-2-135214 and JP-A-2-135215 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") a copolymer obtained by imidation of a styrene-maleic anhydride copolymer with a mixture of primary and secondary diamines such as p-aminophenol and ethylaminoethylamine. It is proposed that these copolymers be used as potential epoxy hardeners. These copolymers also contain ethylamino groups in their side chains. However, the side chain functional groups thus obtained are secondary amino groups. In general, secondary amino groups have less general-purpose properties than primary amino groups. In this respect, these copolymers are not desirable.
Examples of copolymers in which primary amino groups have been probably unexpectedly incorporated partially in their chains include those disclosed in JP-A-64-70595 and JP-A- 64-85246, and U.S. Pat. No. 4,137,185. That is, these copolymers are obtained by reacting a maleic anhydride-grafted ethylene propylene copolymer which is obtained by grafting an ethylene-propylene copolymer with maleic anhydride, with a polyamine containing at least two primary amino groups such as diethylenetriamine, ethlenediamine, and hexamethylenediamine so that it undergoes imidization. However, it is thought that the reaction of a maleic anhydride-grafted ethylene propylene copolymer with a polyfunctional polyamine generally involves a crosslinking reaction not a little during as well as after the reaction. If any crosslinking reaction occurs during the reaction, it may often cause a rise in the viscosity of the reaction mixture and, hence, gelation thereof, disabling the continuance of the reaction.
Therefore, in these conventional techniques, it has been designed to end-cap primary amines present after imidization with acetic anhydride, n-octenylsuccinic anhydride, or the like for the purpose of inhibiting the thickness rise with a lapse of time due to the crosslinking reaction.
Further, JP-A-2-36248 suggests the reaction of an unsaturated acid anhydride-graft modified polyolefin with a diamine. However, this reference gives no clear statement of specific preparation methods and reaction products, and the present inventors' experiences show that crosslinking and gelation are unavoidable according to known methods.
As examples of the reaction of a maleic anhydride copolymer or a maleic anhydride-grafted ethylene propylene copolymer with a primary diamine, there are disclosed methods in JP-A-60-240749, JP-A-64-31864, JP-A-63-146928, JP-A-63-235365, and JP-A-63-199755. However, all these methods are intended for the imide crosslinking of an acid anhydride group with two primary amino groups in a solvent-free resin.
It is theoretically possible to undergo imidization with a primary diamine to form primary amino groups in side chains without causing any crosslinking reaction by raising the molar ratio of primary amino group/succinic anhydride group in the imidation reaction to such an extent that gelation caused by the crosslinking reaction can be subtantially neglected. However, this idea is not practical.
Some of the present inventors previously proposed an improved preparation method which overcomes these drawbacks accompanied by the conventional techniques and a novel copolymer obtained thereby (Japanese Patent Application No. Hei. 3-85735). In this proposal, there is suggested a method which comprises reacting a partial salt of a diamine with an acid, with a succinic anhydride group-containing copolymer and then allowing a base to contact with the reaction product to regenerate an amino group.
It has heretofore been considered to be technically difficult to obtain a copolymer with an excellent hue without causing any crosslinking reaction by allowing diamines to act on a polyfunctional copolymer containing a substituted or unsubstituted succinic anhydride group as a functional group to cause a high-molecular weight modification reaction to incorporate primary amino groups in side chains.
The present invention was worked out to overcome these difficulties.